Germ Layer Theory

The germ layer theory, in the life sciences, is the idea that all embryos are composed of distinct layers which give rise to particular tissues in the adult. It was proposed by Karl von Baer (1792 - 1876) and represented a departure from the previous idea of preformation (see embryology). The theory was extensively modified with the advent of cell theory and evolution theory, but it is still accepted that an embryo has three germ layers. However, these do not originate or develop in the same way in all organisms. RB